Presently, inkjet printers employ two different kinds of inkjet printheads: those which include an integral ink supply and are typically thrown away when the ink supply is exhausted; and those wherein the printhead is connectable to a replaceable container, enabling longer usage of the printhead. In the former type of disposable printhead, typically the printhead is thrown away prior to an occurrence of any printhead failure mechanism. With respect to the latter or "semi-permanent" category of printheads, a number of known failure modes have been experienced.
In printheads which employ heater resistors to cause ejection of droplets of ink, resistor burnout has been a problem. However, redesign of resistor structures and modification of resistor materials has largely eliminated the problem. A further failure mechanism is a buildup of scum within the ink chamber, juxtaposed to the heater resistor. Changes in ink composition are able to largely overcome this problem.
The prior art has suggested that inkjet printheads incorporate a parameter memory for storage of operating parameters to be used by the inkjet printer. Such parameters include: drop generator driver frequencies, ink pressure and drop charging values. Such a printhead is described in "Storage of Operating Parameters in Memory Integral with Printhead", Lonis, Xerox Disclosure Journal, Volume 8, No. 6, November/December 1983, page 503. Other patents have suggested that an ink-containing replaceable cartridge can be provided with an integral memory for storage of information relating to control parameters for a connected inkjet printer. For instance, U.S. Pat. No. 5,138,344 to Ujita stores information on a replaceable ink cartridge which relates to control parameters for the printer. U.S. Pat. No. 5,365,312 to Hillmann et al. describes the use of a memory device integral with an ink reservoir for storage of ink consumption data. European patent EP 0 720 916 describes an ink reservoir which includes a memory for storage of data regarding the identity of the ink supply and its fill level.
It is an object of this invention to provide a replaceable cartridge for use in an ink jet apparatus (i.e. a printer, copier, plotter and the like), which cartridge includes memory with data that enables a projection to be made of further remaining printhead lifetime.
It is another object of this invention to provide an improved method for determining printhead lifetime.